This article explores recent neuroscientific studies on the brains of highly intelligent individuals, revealing that their brains, contrary to common belief, may not be more complex but rather more efficient. Research has shown that high-IQ individuals have fewer, but larger and more complex neurons, particularly in areas like the temporal lobe. These neurons exhibit faster and more stable firing patterns, enabling quicker and more precise information processing. Interestingly, studies also suggest that intelligent brains tend to have lower neurite density and more organized neural fiber arrangements, supporting the "neural efficiency hypothesis"—that smarter brains rely on optimized, less cluttered networks rather than sheer volume. These findings offer new insights into the structural factors that contribute to intelligence.
If you’ve ever wondered what makes the brains of these exceptionally intelligent people different from the average person, let’s break down three fascinating studies to explore the secrets of the "high-IQ brain."
Larger Neurons, Higher IQ
Let’s start with a discovery in the field of neuroscience. A study published in eLife provided some clues at the level of individual brain cells: it turns out that high-IQ individuals have pyramidal neurons in their cerebral cortex that not only have a larger volume and more complex structure, but they also fire faster and more stably.
For decades, scientists have observed that people with higher IQs tend to have thicker gray matter in brain areas such as the temporal and frontal lobes. Gray matter is densely packed with neuronal cell bodies and their dendrites. But a question arises: what is responsible for the increased thickness in the cerebral cortex? Is it more neurons, or are the individual neurons themselves stronger?
Due to the difficulty of directly obtaining healthy brain tissue, this question remained largely unresolved. However, in 2018, a research team from Vrije Universiteit in Amsterdam got a rare opportunity. They obtained small samples of healthy temporal lobe tissue from 46 patients who underwent surgery for epilepsy or brain tumors. These tissue samples were excised from areas close to the lesions but were not themselves pathological.
More importantly, these patients had all completed standard IQ tests (WAIS) and had undergone high-resolution MRI scans. The researchers combined these three data sets:
-
Each individual’s IQ score
-
The cortical thickness of their temporal lobe
-
The 3D structure and electrical activity of individual neurons from their brain tissue
Figure caption: Experimental process
The researchers reconstructed 72 neurons in fine detail and discovered an astonishing pattern—people with higher IQs had neurons with longer dendrites, and these dendrites had more branches. This meant that these neurons could receive signals from a greater number of other neurons.
Moreover, the neurons with "denser" dendritic structures were located in areas where MRI scans showed thicker cortices. In other words, the increased thickness in the cortex was not due to an abundance of small neurons but rather because the neurons themselves were larger and more complex in structure.
The researchers also recorded the electrical activity of 129 neurons and found that neurons in high-IQ individuals had faster and more stable firing rates. For example, during high-load cognitive tasks, the neurons of high-IQ individuals were able to maintain their "bursting" speed more effectively.
Figure caption: IQ score is positively correlated with temporal lobe cortex thickness
Why are larger dendrites associated with faster firing rates? This seems counterintuitive since dendrites primarily receive signals, and firing begins in the axons. In fact, neurons are an integrated electro-physiological system. Larger dendrites act like a bigger "capacitor," enabling the cell’s membrane potential to change more quickly. Computer simulations confirmed this result: neurons with longer dendrites not only generate action potentials faster but can also respond more accurately to high-frequency input signals.
The Simpler Brain Might Be the Smarter One
Now, you might wonder: if larger dendrites make the brain smarter, doesn’t that mean a more complex brain structure is better?
It turns out, that’s not necessarily the case! A research team from Ruhr University Bochum, Germany, published a study in Nature Communications showing that the brains of highly intelligent individuals may actually be more simplified and efficient.
Scientists had long noticed that the brains of smarter individuals tend to be larger, particularly in key regions such as the parietal and frontal lobes. This study sought to go a step further and explore whether there were unique microstructural features in the brains of high-IQ individuals.
To find out, the researchers used multi-shell diffusion tensor imaging (MS-DTI) and matrix reasoning tests. MS-DTI allows us to observe the direction and density of neural fibers in the brain, while the matrix reasoning test measures intelligence.
When analyzing the DTI data, the researchers focused on two indicators in the cortical regions:
-
Neurite density (INVF Cortex)
-
Neurite orientation dispersion (ODI Cortex)
These indicators reflect the density and alignment of the brain’s neural fibers, including axons and dendrites. The results revealed that individuals with higher IQs had lower neurite density and lower orientation dispersion. This means their neural fibers were more orderly and less chaotic.
This discovery supports the "neural efficiency hypothesis," which suggests that intelligent brains don’t rely on "brute force" to operate. Instead, they rely on "efficiency." In other words, the brain networks of high-IQ individuals are organized more efficiently, allowing for faster and more precise information processing.
But here’s the question: Didn’t earlier studies show that more complex dendrites led to a smarter brain? How does this align with the idea that fewer fibers in the brain might be associated with higher IQ?
The key lies in distinguishing between the size of individual neurons and the overall density of neurons in a given area. The Dutch team’s research showed that in high-IQ individuals, individual pyramidal neurons were not only larger but also had more complex dendritic structures. This enhanced the speed of information processing within the neurons themselves.
Meanwhile, the German team’s study measured the overall density of neural fibers (the number of dendrites and axons in a given volume of gray matter). Their finding that high-IQ individuals had lower fiber density complements the Dutch study: while individual neurons are larger and more complex, the overall network of neurons is sparser, potentially facilitating more efficient signal transmission.
Figure caption: Quantifying the structure-function association at the level of a single brain region
Thus, high-IQ brains appear to have a unique structural feature: fewer neurons overall (i.e., lower density, more sparse arrangement), but these neurons are larger and more complex on average. This "sparser network" of "higher-quality units" could create clearer, less cluttered pathways for information transmission, leading to faster and more efficient processing. This is in line with the neural efficiency hypothesis.
The Correlation Between Brain Structure and Intelligence
The two studies mentioned above were conducted in 2018, but more recent research has further explored the relationship between brain structure and intelligence. Early studies focused on specific brain regions like the temporal and frontal lobes, but more recent research shows that higher cognitive functions depend on a coordinated network of various brain regions, including deep structures.
For example, the "default mode network" (DMN) is like the brain's "background program," active when we rest, daydream, or engage in internal thinking. In contrast, the "task-positive network" (TPN) activates when we focus on external tasks.
Importantly, the DMN is not just for "resting"—it plays a crucial role in memory integration, attention regulation, and cognitive flexibility. For example, the posterior cingulate cortex (PCC), a central hub in the DMN, has been found to have strong functional connectivity that correlates with intelligence.
In April 2023, a research team from Baylor College of Medicine in the United States published a study in Brain and Behavior. They analyzed the cortical features of key nodes in both the DMN and TPN—such as cortical thickness and gyrification index (LGI)—to explore their relationship with general intelligence (g-factor).
The study involved 44 healthy young adults and found a significant correlation between cortical thickness and intelligence, particularly in key nodes of the DMN like the right inferior temporal gyrus, ventral posterior cingulate, and parahippocampal gyrus. These regions had thicker cortices in individuals with higher general intelligence.
Additionally, the study found that a higher gyrification index (LGI), a measure of cortical folding complexity, was also linked to higher intelligence. In several nodes of the DMN, such as the right ventral and dorsal posterior cingulate, and the right middle temporal gyrus, higher LGI corresponded with higher intelligence scores.
Figure caption: Relationship between cortical thickness and g factor
The researchers even created a linear regression model using cortical thickness and LGI to predict intelligence scores, explaining 25% of the variance. This suggests that the "intelligence code" might be hidden in the fine structure of networks like the DMN. Thicker cortical regions may indicate more neurons and more complex local connections, while higher gyrification extends the cortical surface area, providing more space for neural computations.
Conclusion
In daily life, we often marvel at certain individuals who seem to think more quickly or learn more easily, almost as if they possess a "super brain." Through neuroscience research, we are beginning to uncover the secrets behind this. It turns out that a "smarter" brain doesn’t necessarily rely on a larger volume or more neurons; rather, it depends on the quality of neurons and the intricate organization of the brain's networks.
However, even if most of us don't have the enviable brains of high-IQ individuals, there is still much we can learn from the analysis of these brains. The quest for "more" may not always be the best solution. Whether it's in knowledge accumulation, skill learning, or life management, focusing on "less" but "better"—focusing on the core, removing distractions, and optimizing structure—might be the key to greater efficiency and excellence.
References:
-
Goriounova NA, Heyer DB, Wilbers R, Verhoog MB, Giugliano M, Verbist C, Ober